Impact of Lamp Choice and H 2 O 2 Dose on Photodegradation of Nitrobenzene

Abstract

Abstract

Nitrobenzene (NB) was spiked into buffered lab water at 5 μM and direct UV and H₂O₂-assisted photodegradation were evaluated using both medium-pressure (MP) and low-pressure (LP) ultraviolet (UV) lamps over a range of UV fluences and H₂O₂ concentrations. MPUV light was found to directly photodegrade nitrobenzene more rapidly than LPUV light, and in both cases loss of NB without UV irradiation (“dark loss”) contributed to the degradation rates. Addition of H₂O₂ improved degradation kinetics, and both LP and MP lamps performed equally as well over industrially relevant hydrogen peroxide doses (1–25 ppm H₂O₂), resulting in a one-log reduction of NB after 300 mJ cm⁻² and 25 ppm H₂O₂. Competition kinetics studies using para-chlorobenzoic acid (pCBA) and molinate as probe compounds were performed to quantify the rate of reaction between target analytes [including NB and three nitrophenol isomers (NPs)] and hydroxyl radicals. Bimolecular rate constants could be used to accurately predict the NB degradation observed in this study. This work helps to clarify the quantum yield for the UV photodegradation of nitrobenzene and reports on the feasibility of utilizing a UV-based oxidation process to destroy a US EPA Contaminant Candidate List chemical of concern.